Oil and gas wells are drilled to produce hydrocarbons from subterranean formations. In recent years, the efficiency of such wells has been improved through recent improvements in fracturing techniques. Fracturing is a process whereby cracks or fissures known as fractures are created in the subterranean formation to enhance the pathways through which the hydrocarbons flow to the oil and gas wells drilled into the formations. Periodically, it is desired to add additional fractures to an already-fractured subterranean formation. For example, additional fracturing may be desired for a previously producing well that has been damaged due to factors such as fine migration. Although the existing fractures may still exist, they have been no longer effective, or less effective. In such a situation, stress caused by the first fracture continues to exist, but it would not significantly contribute to production. In another example, multiple fractures may be desired to increase reservoir production. This scenario may be also used to improve sweep efficiency for enhanced recovery wells such as water flooding steam injection, etc. In yet another example, additional fractures may be created to inject with drill cuttings.
Conventional methods for initiating additional fractures typically induce the additional fractures with near-identical angular orientation to previous fractures. While such methods increase the number of locations for drainage into the wellbore, they may not introduce new directions for hydrocarbons to flow into the wellbore. Conventional methods may also not account for, or even more so, utilize, stress alterations around existing fractures when inducing new fractures.
Creating fractures in horizontal or deviated wells has its own set of challenges. In order to place the most effective fractures in a horizontal well, fractures must be placed transversely in order to drain a much larger formation area. A longitudinal fracture would only drain the similar area slightly more effectively, thus creating a rapid increase of production followed by a rapid production decrease. Essentially, for best drainage of the reservoir, the ideal placement of fractures is generally considered to be radially and generally perpendicular to the horizontal or deviated wellbore. However, radial drainage through these fractures causes severe choking, hence reducing the potential for rapid production during the initial production stages. Other approaches involve creating a fracture that initiates longitudinally, then bending into the natural fracture direction after the fracture extended past the near wellbore stress field influenced region. As the fracture faces move left and right, the longitudinal fracture does not open widely, causing a constriction—a typical characteristic of tortuosity issues. When the natural fracture direction is greater than 30-40 degrees from the wellbore, the fracture tends to rapidly twist and produce multiple, short and narrow fractures. These fractures are narrow as they compete with each other for the fracturing fluid, and therefore, this situation often results in premature screen outs.
When hydra jet assist fracturing methods are used to create transverse fractures, in general, a fracture can be initiated perpendicular to the wellbore (or wherever the jets are directed) and then the fracture will bend into the natural direction of the fracture (unless sophisticated instruments direct the jets towards the natural plane). This generally does not cause tortuosity or screen out issues, as the hydra jet tool will scour the formation face large enough to eliminate tortuosity effects. However, radial inflow to the wellbore constricts production flow, even with this approach.
Accordingly, a need exists for an improved method for initiating multiple fractures in a horizontal or deviated wellbore, where the method accounts for tangential forces around a the wellbore and minimizes constriction of the production flow into the wellbore.